Thermoelectric cooling has been found useful in such diverse applications as CCD cameras, infrared imaging systems and other electro-optic devices, microwave electronic devices, medical instruments, precision temperature controls, laser diodes, and cryoelectronic computer processors. This technology serves well because a unitary component provides cooling for the entire device in a compact form without moving parts and associated mechanical vibrations. At present, the method is cooling capacity limited because the materials in use, primarily semiconducting ceramics such as bismuth telluride are not efficient enough. This limitation confines the practical end-uses to physically smaller devices. Given a thermoelectric material with a higher cooling capacity and efficiency than any currently available, many practical advantages could be achieved. Larger cooling systems could be built replacing those using vapor compression cycles. This would reduce the use of chlorofluorocarbons and their substitutes, reduce the weight and expense of the coolers, and would save energy, all considerations in marine, transportation, consumer, military and industrial applications.
The thermoelectric figure-of-merit, ZT, measures the ability of a material to function in a thermoelectric device. The figure-of-merit is expressed by the well known equation: EQU ZT=S.sup.2 .sigma.T/.kappa.
where;
S=Seebeck coefficient (.mu.V/K) PA1 .sigma.=electrical conductivity ((S/cm; (.OMEGA.-cm).sup.-1)) PA1 .kappa.=thermal conductivity (W/cm K) PA1 T=temperature (K) PA1 i) a conductive polymer characterized by a high inherent Seebeck coefficient and a low inherent thermal conductivity; and PA1 ii) an effective amount of nanometer-sized metal particles dispersed into and intimately associated with said polymer to establish a nanophase metal/polymer composite material;
Despite three decades of effort, only small increases in the figure-of-merit for semiconducting ceramic materials have been attained (Mahan G. et al.; Physics Today, 3/97; p 42). The ZT for the best inorganic semiconductors such as Bi.sub.2 Te.sub.3 is about 1. In commercial practice, the value ranges between 0.7 and 0.9. The best organic conductors such as polythiophene have ZT very much less than 1 even though these materials may have Seebeck coefficients greater than one thousand. Their problem is low electrical conductivity. For example, the electrical conductivity of undoped polythiophene is 10.sup.-11 (.OMEGA.-cm).sup.-1.
It is clear that large values of Seebeck coefficient and of electrical conductivity are desired. Unfortunately, in known materials, increases in Seebeck coefficient are associated with reduction in conductivity and vice versa.
Howell investigated a number of conjugated, conducting polymers (see Technical Report, Howell B., "Thermoelectric Properties of Conducting Polymers", CARDIVNSWC-SSM-64-94/Jul. 12, 1994) because these have small values for thermal conductivity, low density, moderate electrical conductivity and some have moderately large Seebeck coefficients. The term "conjugated" above refers to polymers whose backbone consists of (1) single bonds alternating with (2) unsaturated groups such as double bonds, triple bonds, or aromatic groups. Tests of a number of conducting, conjugated, polymers including polyacetylene, polyacenes, polyaniline, polyparaphenylene and polyparaphenylenevinylene, polyphenylene sulfide, polypyrrole, polythiophene, and Schiff's Bases were carried out along with various additions (carbon, iodine, tetraethylamineammonium tetrafluoroborate, potassium persulfate and ferric chloride). These materials did not yield the desired improvement in thermoelectric figure-of-merit. In U.S. Pat. No. 5,472,519, Howell et al. disclose using poly-3-octylthiophene and ferric chloride in a respective molar ratio of approximately 2:1 as a thermoelectric material. The figure-of-merit so obtained, 0.007, shows a modest increase over the prior art for doped conducting polymers but other known semiconductor materials, e.g. Bi.sub.2 Te.sub.3, approach 1.0.
It is an object of the instant invention to provide a composition of matter having a significantly higher ZT than that of presently known materials and to establish methods of making and using this composition of matter.
It is a further object to provide thermoelectric devices, based on the novel composition of matter, that will have hitherto unachievable efficiency.